Piercing apparatus

ABSTRACT

A piercing apparatus compact in size having a decreased number of hoses is suited for use as an iron runner port-opening machine for a blast furnace or the like furnace in an iron mill. The piercing apparatus executes the piercing by moving back and forth, by using a feed unit, a drifter equipped with a forward-blowing unit, a reverse-blowing unit and a rotary unit, and wherein cylinders containing a cylindrical blowing piston are provided in front of, and at the back of, a drifter body maintaining a distance relative to each other; a shank rod having, formed as a unitary structure, a blowing portion of a large diameter with blowing surfaces formed on the front and rear portions thereof and rod-like small-diameter portions protruding forward and backward beyond the blowing portion, is provided along the axial direction of the drifter body in a manner that the blowing portion is positioned between the front cylinder and rear cylinder and that the small-diameter portions on both sides are fitted to the cylindrical blowing pistons of the respective sides; and valves are provided in the outer peripheral portions of the front and rear cylinders to supply hydraulic pressure into the cylinders.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a piercing apparatus suited foruse as an iron runner port-opening machine for a blast furnace, or thelike furnace, in an iron and steel factory.

[0003] 2. Description of the Related Art

[0004] As an iron runner port-opening machine for a blast furnace, orthe like furnace, in general, there has been widely used a hydraulicdrifter having a cylinder for slidably holding a piston that moves backand forth, and a sleeve for holding a shank rod attached to a frontportion of the cylinder, so that the piston is advanced by the hydraulicpressure supplied to the cylinder to blow the shank rod. A piercing rodis joined to an end of the shank rod, and a bit is attached to an end ofthe piercing rod to execute the piercing. During the piercing operation,a thrust is imparted to the drifter by a feed unit provided on a supportunit that supports the drifter. when the piercing is effected to adesired depth, the drifter is moved back to withdraw the piercing rodand the bit from the hole that is pierced. In this case, however, therefrequently occurs an accident, i.e., a so-called jamming in which thebit is not easily withdrawn as the pierced hole is stuffed with thepulverized scraps on the back side of the bit.

[0005] In order to easily withdraw the bit and the rod despite such anaccident has occurred, there has been already developed a hydraulicpiercing apparatus equipped with a reverse-blowing unit to give abackward blow to the rod (Japanese Patent No. 2613538). The piercingapparatus equipped with the reverse-blowing unit has been widely usedfor opening the iron runner port of a blast furnace, since it makes itpossible to relatively easily withdraw the rod by actuating thereverse-blowing unit when the rod cannot be withdrawn. On the site ofwork of this kind, however, much limitation is imposed on the workingspace, and it has been urged to provide a more compact piercingapparatus. Besides, the above conventional piercing apparatus requiresat least five thick hydraulic hoses for operating the piercingapparatus, i.e., a hydraulic hose for forward blowing, a hydraulic hosefor reverse blowing, a hydraulic hose for forward rotation, a hydraulichose for reverse rotation, and a return hydraulic hose for forward andreverse blows, resulting in a complex external structure and hinderingthe operability.

SUMMARY OF THE INVENTION

[0006] It is therefore a requirement of the present invention to providea piercing apparatus which is compact in size and uses a decreasednumber of hoses as a result of improving the above-mentionedconventional forward/reverse blow-type piercing apparatus.

[0007] In order to solve the above assignment, the present inventionemploys the following constitution. That is, the piercing apparatus ofthe invention executes the piercing by moving, back and forth by using afeed unit, a drifter equipped with a forward-blowing unit, areverse-blowing unit and a rotary unit; wherein

[0008] cylinders containing a cylindrical blowing piston are provided infront of, and at the back of, a drifter body maintaining a distancerelative to each other;

[0009] a shank rod having, formed as a unitary structure, a blowingportion of a large diameter with blowing surfaces formed on the frontand rear portions thereof and rod-like small-diameter portionsprotruding forward and backward beyond the blowing portion, is providedalong the axial direction of the drifter body in a manner that theblowing portion is positioned between the front cylinder and rearcylinder and that the small-diameter portions on both sides are fittedto the cylindrical blowing pistons of the respective sides; and

[0010] valves are provided in the outer peripheral portions of the frontand rear cylinders to supply hydraulic pressure into the cylinders.

[0011] The rotary unit can be constituted in a relatively compact sizeif a spline is formed in the outer peripheral portion of the blowingportion of the shank rod, and if a chuck that transmits the rotation, bybeing spline-fitted to the blowing portion, is rotated by the rotaryunit provided on the outer peripheral portion of the drifter body.

[0012] Further, a pilot valve unit is provided on the outer peripheralportion of the drifter body to selectively change the hydraulic pressurefor blowing over to the valve for forward blowing or over to the valvefor reverse blowing, and is changed over by the hydraulic pressuresupplied to the feed unit in a manner that the hydraulic pressure issupplied to the valve for forward blowing by the hydraulic pressure formoving the feed unit forward and that the hydraulic pressure is suppliedto the valve for reverse blowing by the hydraulic pressure for movingthe feed unit backward. Then, the forward blow and the reverse blow areautomatically changed over depending upon the change-over of the feed.

[0013] It is desired that a pilot valve unit for selectively changingthe hydraulic pressure for rotation, over to the valve for forwardrotation or over to the valve for reverse rotation, is provided on theouter peripheral portion of the drifter body from the standpoint ofshortening the conduits and decreasing the size.

[0014] In the above piercing apparatus, it is desired to install, in aheat-resistant box, a valve for changing over all or part of thehydraulic pressure supplied to the blowing unit, rotary unit and feedunit and a valve for controlling the flow rate and pressure, and toinstall a cooling unit for forcibly cooling the interior of theheat-resistant box by purging the air as means for cooling theheat-resistant box. With the valve unit being installed near a guidecell for moving the drifter, the valve system can be constituted in acompact size. Similarly, it is desired to install, in a similarheat-resistant box, a valve for changing over all or part of thehydraulic pressure supplied to the blowing unit, rotary unit, feedingunit and to the pilot valve that changes over the direction of theblowing unit and the rotary unit, as well as to install a control valvefor controlling the flow rate and pressure.

[0015] It is further desired from the standpoint of compactly arrangingthe hydraulic conduits that a return hydraulic pressure from theforward-blowing unit and the reverse-blowing unit meet a returnhydraulic pressure from the rotary unit and/or the feed unit through thevalve unit, so that the return hydraulic pressure is returned to a fluidtank through a common hydraulic hose.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a vertical sectional view of a drifter according to anembodiment of the invention and illustrates a portion thereof in anexpansion plan;

[0017]FIG. 2 is a plan view of FIG. 1;

[0018]FIG. 3 is a side view of FIG. 1;

[0019]FIG. 4 is a back view of FIG. 1:

[0020]FIG. 5 is a sectional view along X-X of FIG. 2;

[0021]FIG. 6 is a diagram schematically illustrating hydraulic conduits;

[0022]FIG. 7 is a diagram schematically illustrating hydraulic conduitsdifferent from those of FIG. 6;

[0023]FIG. 8 is a diagram schematically illustrating hydraulic conduitsfurther different from those of FIG. 6;

[0024]FIG. 9 is a view schematically illustrating the principle ofoperation of a piston;

[0025]FIG. 10 is a view schematically illustrating the principle ofoperation of the piston;

[0026]FIG. 11 is a view schematically illustrating the principle ofoperation of the piston;

[0027]FIG. 12 is a view schematically illustrating the principle ofoperation of the piston;

[0028]FIG. 13 is a view schematically illustrating the principle ofoperation of the piston;

[0029]FIG. 14 is a plan view illustrating an example of using a piercingapparatus of the invention as an iron runner port-opening machine; and

[0030]FIG. 15 is a side view of FIG. 14.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0031] Hereinafter, an embodiment of the invention will be concretelydescribed. The drawings illustrate an embodiment of the inventionwherein, as shown in FIG. 1, a main body 2 of a drifter 1 of thepiercing apparatus is provided with a cylinder 3 for forward blowing anda cylinder 4 for reverse blowing arranged in series at a predetermineddistance. Bushings 6 and 7 are provided at both front and rear ends ofthe cylinder 3 for forward blowing, and a hollow rear cap 5 in the shapeof a bag is secured by bolts to the rear portion of the cylinder 3. Abushing 9 is provided in the inner surface of the rear cap 5.

[0032] An intermediate cylinder 10 is connected between the cylinder 3for forward blowing and the reverse-blowing unit. A chuck driver 13having a tooth train 13 a formed on the outer peripheral surface thereofis rotatably supported by bush in the inner periphery of theintermediate cylinder 10, and a chuck 15 is fitted into the chuckdriver. The chuck 15 is divided into two chuck pieces 15 a, 15 a ofnearly a fan shape, and a female spline 15 c is formed in the innersurface of each of the chuck pieces 15 a, 15 a. On the inner surface ofthe chuck driver 13 are formed protuberances 13 a, 13 a protruding inthe direction of diameter, and the chuck pieces 15 a, 15 a, of nearly afan shape fitted in the chuck driver, are brought into contact therewithso as to be coupled and secured.

[0033] Bushings 16, 17 are provided at both front and rear ends of thecylinder 4 for reverse blowing connected to the front side of theintermediate cylinder 10, and a front head 19 having bushings 18, 19provided in the inner surface side thereof is attached to the front sideof the cylinder.

[0034] A rod-like shank rod 20 is inserted in the main body 2 of thedrifter 1. The shank rod 20 is provided with a junction portion 22 of alarge diameter having an internally threaded portion 22 a, and isfurther provided with a blowing portion 23 of a large diameter at theintermediate portion thereof and with a slide portion 24 at the rear endthereof. A gap portion 20 a between the junction portion 22 and theblowing portion 23, and a gap portion 20 b between the side portion 24and the blowing portion, are in the form of a round rod of a smalldiameter.

[0035] The blowing portion 23 of the shank rod 20 is formed nearly inthe shape of a drum, both the front surface 23 b and the rear surface 23a thereof serving as blowing surfaces. A male spline 25 is formed on theouter periphery of the blowing portion 23 and is fitted to the femalespline 15 c of the chuck.

[0036] A cylindrical piston 30 for forward blowing is fitted onto theround rod portion 20 b on the rear side of the shank rod 20, and acylindrical piston 33 for reverse-blowing is fitted onto the round rodportion 20 a of the front side. A small gap t is maintained betweenthese pistons and the round rod portion, so that the pistons are allowedto freely move back and forth.

[0037] The piston 30 for forward blowing and the piston 33 for reverseblowing have an equal size but are directed opposite to each other.Further, the cylinders 3 and 4 containing these front and rear pistonshave the same shape and the same size, but are directed opposite to eachother. Valve units 40, 43 for actuating the pistons are mounted on theouter peripheries of the cylinder 3 for forward blowing and of thecylinder 4 for reverse blowing.

[0038] A pilot valve unit 45 for blowing is mounted on the upper surfaceon the outer periphery of the intermediate cylinder 10 of the drifter 1,and a rotary pilot valve unit 47 for changing the rotation over to theforward direction or the reverse direction is mounted on the sidesurface thereof. In FIG. 1 illustrating the operation system, the rotarypilot valve unit 47 is shown in an expansion plan for the purpose ofconvenience and, hence, the two pilot valve devices 45 and 47 are shownbeing overlapped one upon the other. A rotary unit 50 is provided on theside surface of the intermediate cylinder 10 on the side opposite to thepilot valve unit 47. The rotary unit 50 includes a hydraulic motor 51and a counter gear 52, the counter gear being in mesh with the toothtrain 13 a of the chuck driver 13, so that the rotation of the hydraulicmotor 51 is transmitted to the chuck driver 13 through the counter gear52.

[0039] Next, actions of the pilot valve units 45, 47 will be describedbased on the diagram of operation system. In the case of forwardblowing, first, a high-pressure fluid enters into the pilot valve unit45 for blowing through a port Pa when the drifter 1 moves forward andenters into the valve unit 40 for forward blowing passing through a portPf to actuate the piston 32 for forward blowing. The return fluid atthis moment is returned back to the fluid tank through port Pg, port Phand port Pc.

[0040] In the case of the reverse blowing, the high-pressure fluidenters into the pilot valve unit 45 for blowing through the port Pa whenthe drifter 1 moves back. In this case, the pressurized fluid acts uponthe pilot port Pd from a feed-backward circuit for moving the drifter 1backward. When the pressurized fluid overcomes the pushing force of thespring 59, the valve 60 is changed over, and the pressurized fluid fromthe port Pa enters into the valve unit 43 for reverse blowing passingthrough the port Pi to actuate the piston 33 for reverse blowing. Atthis moment, the return fluid is sent back to the fluid tank throughport Pj, port Ph and port Pc.

[0041] In the case of the forward rotation, the high-pressure fluidenters into the pilot valve unit 47 for rotation through the port Pbduring the piercing, and reaches a forward rotation port P1 of thehydraulic motor 51 through the port Pk to rotate the shank rod 20forward. In this case, the return fluid enters into the port Pn from thereverse rotation port Pm of the hydraulic motor 51, meets the returnfluid from the blow return port Ph, and is returned back to the fluidtank through port Pc.

[0042] The reverse rotation is used for removing the rod fitted into thethreaded portion of the junction portion of the shank rod 20. In thiscase, the high-pressure fluid enters into the pilot valve unit 47 forrotation at the feed-backward end through the port Pb and, at the sametime, the fluid pressurized high enough to overcome the pushing force ofthe spring 61 acts on the pilot port Pe through the pilot port Pd,whereby the valve 65 is changed over, so that the pressurized fluidarrives at a reverse rotation port Pm of the hydraulic motor 51 throughport Pb and port Pn thereby to rotate the shank rod 20 in reverse. Thereturn fluid at this moment enters into the port Pk from the forwardrotation port P1 of the hydraulic motor 51, enters the blow return portPh, and is returned back to the fluid tank through port Pc.

[0043] FIGS. 6 to 8 are diagrams of hydraulic conduits for operating thepiercing apparatus 1, wherein local constitutions are slightly differentdepending upon the drawings. The drawings of these conduits do notinclude the conduits for swinging, moving up and down or centering upand down, the guide cell on which the drifter is mounted. As shown, thepiercing apparatus 1 is provided with three thick hydraulic hoses, i.e.,a hydraulic pressure feed hose (blow IN) Hi for blowing and rotating thedrifter, a hydraulic pressure feed hose for rotation (rotation IN) Hr,and a return line (T-line) Ht returning from the blowing unit and therotary unit. Further, to the feed unit for moving the drifter forwardand backward, are connected two hydraulic hoses, i.e., a hydraulic hoseHa for feed forward and a hydraulic hose Hb for feed backward.

[0044] In the example of conduits of FIG. 6, a narrow pilot hose Hp forchanging over the forward/reverse blow is connected to the conduit forfeed backward, whereby a pilot pressure acts from the line of feedbackward on the pilot valve Vp for changing over the forward/reverseblow so that, at the time of moving back, the blow is automaticallychanged over to the reverse blow. The rotation is usually in the forwarddirection. When the reverse rotation is required, a forward/reversechange-over solenoid valve Vs of the valve unit provided in the valvestand is turned on, thereby to obtain the rotation in the reversedirection.

[0045]FIG. 7 illustrates an example of conduits different from the aboveexample. In this example of conduits, a narrow pilot hose Hp from theconduit for feed backward is connected to the valve Vs for changing overthe rotation and to the pilot valve Vp for changing over theforward/reverse blow so that, when the load is exerted during the feedbackward, the blow is automatically changed from the forward blow overto the reverse blow and the rotation is changed from the forwardrotation over to the reverse rotation. In general, the reverse blow isrequired at the time of withdrawing the rod (metal rod) or when the loadis exerted during the feed backward, In order to prevent the screws frombeing loosened at the coupling portions, the drifter is rotated forward.And a some degree of pressure is applied to the circuit for forwardrotation and, besides, the valve spring sp produces a force. Therefore,the forward rotation is not changed over to the reverse rotation by thepilot pressure in the feed-backward circuit. The drifter must be rotatedin reverse at the time when the operation is finished and the rod (metalrod) must be removed. In this case, the feed is brought to the backwardlimit, and the drifter is rotated in a state where the solenoid valvefor backward motion is turned on (in a state where the pressure isexerted on the backward circuit); i.e., the drifter is rotated in thereverse direction. The method of FIG. 7 minimizes the number of conduitsbetween the valve stand and the drifter.

[0046]FIG. 8 illustrates a further different example of the conduits. Inthis example of the conduits, the pilot valve for changing over theforward-reverse blow/forward-reverse rotation is actuated by anelectromagnetic valve in the valve stand. According to this method, theindividual modes are selected relying on the combinations of operationsof the electromagnetic valves. Then, the forward/reverse blow and theforward/reverse rotation can be arbitrarily selected and executed.

[0047] Next, the blowing operation of the drifter 1 will be describedwith reference to the drawings. FIGS. 9 to 13 illustrate thereverse-blowing unit. In FIG. 9, the piston 33 is reaching the top deadcenter (front end position) and the high-pressure fluid acts on a rearpiston chamber S1 from a high-pressure port D1. There is a relationshipM1>M2 between the pressure-receiving area M1 of the rear piston chamberS1 and the pressure-receiving area M2 of a front piston chamber S2. Asthe high-pressure line is communicated with the rear piston chamber S1,therefore, a force acting on the rear part of the piston becomes largerthan a force acting on the front part of the piston, and the pistonenters into the blowing stroke and moves forward (moves toward the rightin the drawing).

[0048] In FIG. 10, the piston 33 continues to move forward and duringthis period, the accumulator A supplies the lacking amount of operationfluid. The piston further proceeds, and the large diameter portion 33 athereof opens the valve change-over port D3 so that it is communicatedwith a port D2 of the low-pressure line LP. Then, the pressure in thevalve change-over chamber S4 decreases and the valve V starts changingover.

[0049] In FIG. 11, the piston 33 reaches a point of reverse blow,transmits the kinetic energy which it has gained during the stroke ofreverse blow to the shank rod 20 which then transmits the energy ofreverse blow to the bit. At this moment, the valve V has been completelychanged over, whereby the ports (D1, D2, D3) are all communicated withthe low-pressure line LP, the force acting on the front part of thepiston 33 becomes larger than the force acting on the rear part of thepiston, and the piston enters into the stroke of moving backward. As thepiston further moves forward beyond the point of reverse blow with noload, the piston closes the port D5, comes into a halt while forming acushion chamber S3 and, then, starts moving backward.

[0050] In FIG. 12, the piston 33 continues to move backward, and thelarge diameter portion 33 a opens the valve change-over port D4 so thatit is communicated with the port D5 of the high-pressure line HP. Then,the pressure is elevated in the valve change-over chamber S4, and thevalve V starts changing over.

[0051] In FIG. 13, the piston 33 for reverse blow continues to movebackward and the valve V continues to be changed over. Then, the port D1is communicated with the high-pressure line HP, and the high-pressurefluid enters into the rear piston chamber. Due to the inertial energywhich the piston has gained during the stroke of backward movement, therear piston chamber forms a cushion chamber in the high-pressure line,and the hydraulic pressure is accumulated in the accumulator A. As thevalve V is completely changed over and the piston reaches the top deadcenter at where it is stopped by the cushion, the initial state of FIG.7 is resumed.

[0052] The foregoing description has dealt with the operation of thereverse-blowing unit. The same, however, also holds for the case of theforward-blowing unit (the direction is reversed) which, therefore, isnot described here.

[0053]FIGS. 14 and 15 illustrate an example of using the piercingapparatus M as an iron runner port-opening machine for a blast furnaceF, wherein the drifter 1 of the piercing apparatus M is attached to theguide cell 71 in a manner to move back and forth. The base portion ofthe guide cell 71 is supported by an arm 73 hanged from a swing base 72via a shaft 74 so as to freely rotate up and down, and an intermediateportion thereof is supported by a lift unit 75. Reference numeral 77denotes a hydraulic cylinder for lifting. Upon expanding and contractingthe hydraulic cylinder 77, the guide cell turns up and down with theshaft 74 as a center. In the drawing, reference numeral 79 denotes afive-way swivel for the air and water, and 80 denotes an up-downcentering unit for centering the guide cell in the up-and-downdirection. The position of the end of the guide cell is adjusted in theup-and-down direction by forwardly or reversely rotating an air motor 81for accomplishing the centering in the up-and-down direction.

[0054] In the drawing, reference numeral 85 denotes a hydraulic feedmotor constituting a feed unit F attached to the guide cell 71. When thehydraulic feed motor 85 is rotated forward or reverse, a sprocketattached to the rotary shaft of the motor rotates, and a chain wrappedround the sprockets attached to the front end and the rear end of theguide cell moves back and forth. A carriage 87 is attached to the chain,and the drifter 1 is mounted on the carriage. Therefore, the drifter 1moves back and forth accompanying the motion of the chain. Referencenumeral 90 denotes a pump unit, 91 denotes a valve unit (containing asmall manifold electromagnetic block) for the drifter, 92 denotes avalve unit containing an electromagnetic valve block for the liftingunit for raising and lowering the guide cell 71, reference numeral 93denotes a valve stand mounting a valve unit for swinging, 95 denotes asafety hook rotated by an air cylinder 95 a, reference numeral 96denotes an air electromagnetic valve box, and 97 denotes an encoder fordetecting the depth of the hole.

[0055] The valve unit 91 for the drifter is the one in which the valvefor changing over whole or part of the hydraulic pressure supplied tothe blowing unit, rotary unit and feed unit, and the valve forcontrolling the flow rate and pressure, are installed in aheat-resistant box mounted on the guide cell, and is provided withcooling means for forcibly cooling the interior of the heat-resistantbox by purging the air or a like method. The valves that are containedin the box having resistance against the heat are protected from hightemperatures when the apparatus is used for opening the iron runningport of the blast furnace and, besides, the apparatus is realized in acompact size. It is further desired to contain, in the aboveheat-resistant box, the valve for changing over whole or part of thehydraulic pressure supplied to the pilot valve that changes over thedirections of the blowing unit and of the rotary unit, as well as thevalve for controlling the flow rate and pressure.

[0056] To use the piercing apparatus M as the iron running port-openingmachine, a piercing rod R is connected to the shank rod 20 of thedrifter 1, and a bit is attached to the end of the piercing rod. Thedirection and inclination of the drifter 1 are so adjusted that the bitcomes in contact with a desired piercing portion, the feed unit isactuated to fit the bit to the piercing position (e.g., iron runningport Fa of the blast furnace), and the forward-blowing unit and therotary unit are actuated. Thus, the piercing operation is executed asdesired.

[0057] After the piercing is effected to a predetermined depth, thedrifter 1 is moved backward to withdraw the bit and the rod from thehole that is pierced. At this moment, the feed unit is changed over tothe side of moving backward, whereby the pilot valve unit 45 operates,and the supply of hydraulic pressure for blowing is changed from thevalve for forward blowing over to the valve for reverse blowing. Thus,the blowing is changed from the forward blow which gives blow to the rodin the forward direction over to the reverse blow which gives blow inthe reverse direction. Even in case the bit cannot be withdrawn due tothe pieces and scraps of the piercing operation in the hole on the backside of the bit, the blow in the reverse direction helps to easilywithdraw the bit.

[0058] The hydraulic pressure can be supplied from the hydraulic pump tothe drifter 1 by using the hydraulic hose for forward blowing and thehydraulic hose for reverse blowing, and the return fluid from theblowing unit and the return fluid from the rotary unit are returned backto the fluid tank through the common hydraulic hose, making it possibleto decrease the number of thick hydraulic hoses extending along theouter side, and the apparatus is realized in a compact size featuringeasy operation. In the diagramed drifter, further, the rod connectionportion of the shank rod is internally threaded enabling the externalthread of the piercing rod to be directly screwed therein and connected.Compared to the prior art using a coupling sleeve, therefore, theblowing force can be efficiently transmitted. However, this portion maybe constructed similarly to that of the prior art.

[0059] According to the piercing apparatus of the present invention asdescribed above, the shank rod having, in the intermediate portionthereof, a blowing portion with blowing surfaces on the front and rearsides thereof, is used as a shank rod of the drifter, cylindricalpistons are fitted to the front and rear sides of the blowing portion toapply forward/reverse blow by the pistons on the front and rear sidesthereof. Therefore, the overall length is decreased to realize theapparatus in a compact size. Further, the pilot valve is provided forchanging over the forward blow and the reverse blow. At the time whenthe device for feeding the drifter is changed over to the side ofbackward motion, the pilot valve is operated to change the forward blowover to the reverse blow. Accordingly, the hydraulic pressure feed (IN)hose can be used in common for the forward blow and for the reverseblow. Further, the return circuits of the blow and rotation are formedas a T-line, and the return fluids of the blow and rotation are returnedback to the tank through the common return hose. Therefore, only threethick hoses are required, contributing to simplifying the externalstructure and improving the operability.

1. A piercing apparatus for executing piercing by moving back and forth,by using a feed unit, a drifter equipped with a forward-blowing unit, areverse-blowing unit and a rotary unit, wherein: cylinders containing acylindrical blowing piston are provided in front of, and at the back of,a drifter body at a distance relative to each other; a shank rod having,formed as a unitary structure, a blowing portion of a large diameterwith blowing surfaces formed on the front and rear portions thereof androd-like small-diameter portions protruding forward and backward beyondthe blowing portion, is provided along the axial direction of thedrifter body in a manner that the blowing portion is positioned betweenthe front cylinder and rear cylinder and that the small-diameterportions on both sides are fitted to the cylindrical blowing pistons ofthe respective sides; and valves are provided in the outer peripheralportions of the front and rear cylinders to supply hydraulic pressureinto the cylinders.
 2. A piercing apparatus according to claim 1,wherein a chuck that transmits the rotation being spline-fitted to theblowing portion, is rotated by the rotary unit provided on the outerperipheral portion of the drifter body.
 3. A piercing apparatus forexecuting the piercing by moving, back and forth by using a feed unit, adrifter equipped with a forward-blowing unit, a reverse-blowing unit anda rotary unit, wherein a pilot valve unit is provided on the outerperipheral portion of the drifter body to selectively change thehydraulic pressure, for blowing, over to the valve for forward blowingor over to the valve for reverse blowing.
 4. A piercing apparatus forexecuting the piercing by moving back and forth, by using a feed unit, adrifter equipped with a forward-blowing unit, a reverse-blowing unit anda rotary unit, wherein a pilot valve unit is provided on the outerperipheral portion of the drifter body to selectively change thehydraulic pressure, for rotation, over to the valve for forward rotationor over to the valve for reverse rotation.
 5. A piercing apparatusaccording to claim 3, wherein the pilot valve selectively changes overthe supply of hydraulic pressure for blowing by utilizing the hydraulicpressure supplied to the feed unit in a manner that the hydraulicpressure is supplied to the valve for forward blowing by the hydraulicpressure for moving the feed unit forward and that the hydraulicpressure is supplied to the valve for reverse blowing by the hydraulicpressure for moving the feed unit backward.
 6. A piercing apparatusaccording to claim 1 or 2, wherein an end portion of the shank rodattached to the drifter is internally threaded, and the base portion ofa piercing rod extending from the drifter is screwed into the internallythreaded portion and is connected thereto.
 7. A piercing apparatus forexecuting the piercing by moving back and forth, by using a feed unit, adrifter equipped with a forward-blowing unit, a reverse-blowing unit anda rotary unit, wherein a valve for changing over whole or part of thehydraulic pressure supplied to the blowing unit, rotary unit and feedunit and a valve for controlling the flow rate and pressure, areinstalled in a heat-resistant box, and a valve unit provided withcooling means for forcibly cooling the interior of the heat-resistantbox is mounted near a guide cell that moves the drifter.
 8. A piercingapparatus, wherein a valve for changing over whole or part of thehydraulic pressure supplied to the blowing unit, rotary unit, feed unitand to a pilot valve for changing over the directions of the blowingunit and the rotary unit, as well as a valve for controlling the flowrate and pressure, are installed in a heat-resistant box, and a valveunit provided with cooling means for forcibly cooling the interior ofthe heat-resistant box is mounted near a guide cell that moves thedrifter.
 9. A piercing apparatus according to claim 7 or 8, wherein areturn hydraulic pressure from the forward-blowing unit and thereverse-blowing unit meet a return hydraulic pressure from the rotaryunit and/or the feed unit through the valve unit, so that the returnhydraulic pressure is returned to a fluid tank through a commonhydraulic hose.